Federal courts must determine the prejudicial impact of constitutional error in state court trials under the Brecht standard of “substantial and injurious effect.” At appellant’s murder trial, the trial court excluded the testimony of a defense witness. On appeal from his conviction, appellant argued that the exclusion of the witness’s testimony violated Chambers v. Mississippi which held that a combination of erroneous evidentiary rulings rose to the level of a due process violation. The appellate court held that “no possible prejudice” could have resulted in light of the cumulative nature of the witness’s testimony. The federal court found the state appellate court’s failure to recognize Chambers error an unreasonable application of clearly established law, and disagreed with the finding of “no possible prejudice.” However, it concluded that there was an insufficient showing that the improper exclusion of the testimony had a substantial and injurious effect on the jury’s verdict under Brecht v. Abrahamson, and denied relief. The United States Supreme Court held that a federal court must assess the prejudicial impact of constitutional error in a state court criminal trial under Brecht’s “substantial and injurious effect” standard whether or not the state appellate court recognized the error and reviewed it for harmlessness under Chapman.